This application is based upon Japanese Patent Application Nos. Hei. 11-66949 filed on Mar. 12, 1999, and 2000-52165 filed on Feb. 23, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to pressure detection apparatuses, and particular to a pressure detection apparatus in which a pressure detection chamber for containing a sensor element is manufactured by assembling a first case and a second case and is liquid-tightly sealed by an O-ring sandwiched between the first case and the second case (O-ring sealing type), the method of manufacturing the same, and a molding apparatus for manufacturing the same.
2. Related Art
Conventional pressure detection apparatuses of this type (O-ring sealing type) have been proposed in JP-A-7-209115 and JP-A-243926. These documents have proposed: a seal diaphragm type semiconductor pressure detection apparatus, which aims at a decreasing of the number of parts, a simplification of the manufacturing step, and an improvement of reliability; and a manufacturing method of the same. These pressure detection apparatuses are mainly used for detecting a pressure within a range of 0-10 MPa, for example, a coolant pressure of an air-conditioner for vehicles or a pressure of a power steering oil of a vehicle.
It can be thought that this type of the pressure detection apparatus is applicable to the other purpose such that for detecting pressure of a brake oil or high-pressured fuel oil. In these purposes, the pressure detection sensor is used for detecting a high pressure within a range of 0-20 MPa. However, according to an experimental result, it is found that the O-ring for liquid-tightly sealing the pressure detection chamber may be damaged.
A mechanism of occurrence of the damage is further analyzed. FIG. 13A shows a schematic sectional view of an O-ring sealing type pressure detection apparatus (related art), which is manufactured by modifying the above-described conventional method, and FIG. 13B shows an enlarged sectional view of a circle XIIIB in FIG. 13A. A pressure detection chamber J5 is formed by assembling a resin case (first case), which is formed by molding and includes a connector pin J1, and a metallic housing (second case), which includes a seal diaphragm J3. A sensor element J6 is contained in the pressure detection chamber J5 by being fixed to a seat.
Furthermore, oil J7 is filled in the pressure detection chamber J5 for transmitting pressure from the seal diaphragm J3. At an outer peripheral portion of the pressure detection chamber J5, a grove (O-ring groove) is formed at an end surface of the resin case J4. An O-ring J8 is provided in the O-ring groove so that the O-ring is sandwiched by a press member J9, which is a part of the housing J4, and the resin case J2. The pressure detection chamber J5 is liquid-tightly sealed by the O-ring J8.
This kind of pressure detection apparatus is generally formed as follows. At first, the resin case J2 is formed by molding. The pressure detection chamber J5, which contains the sensor element J6 therein, is formed by assembling the resin case J2, in which the oil J7 is filled in a depression portion as the pressure detection chamber J5, and the housing J4. At the same time, the O-ring is sandwiched by the case J2 and the housing J4 at the outer peripheral portion of the pressure detection chamber J5 with being pressed. Furthermore, the case J2 and the housing J4 are fixed and assembled by caulking. In this way, a basic structure of the pressure detection apparatus is formed.
According to this apparatus, when a pressure to be detected is applied to the pressure detection chamber J5, the O-ring J8 is pressed toward an arrow in FIG. 13B. However, movement of the O-ring J8 toward outer peripheral direction is restricted by an outer sidewall surface J10. That is, the outer sidewall surface J10 acts as a wall portion for restricting the O-ring. In this time, the O-ring J8 is squeezed into a gap between the outer sidewall surface J10 and the press member J9.
Here, according to this related art, when the pressure to be detected is within 0-10 MPa, a degree of squeezing of the O-ring J8 to the gap is that as shown by a dotted line in FIG. 13B. However, when the pressure to be detected becomes high such as around 20 MPa, a degree of squeezing is increased as that shown by a solid line in FIG. 13B, so that the O-ring J8 is deformed. As a result, at a tip portion of a squeezed portion, tensile stress is undergone toward a direction shown by an arrow Y, so that crack may occur in the tip portion. When the pressure to be detected is repeatedly changed, the crack may advance, so that the O-ring J8 may be damaged.
The damage of the O-ring may determinate a sealing ability of the pressure detection chamber J5, and may decrease reliability of the apparatus. Here, similar inconvenience may occur at a gap between the wall portion and the end surface of the resin case J2, when the wall portion for restricting the O-ring is provided at the housing J4 side instead of the resin case J2. Furthermore, the similar inconvenience may occur, when a metallic case is applied instead of the resin case J2, as long as the case J2 is formed by being pressed or forged.
In other words, when the above-described wall portion is provided at least one of the first case and the second case being assembled with the first case, the inconvenience, in which the O-ring may be damaged due to squeezing of the O-ring to the gap between the first case and the second case, may occur.
This invention has been conceived in view of the background thus far described and its object is to prevent an O-ring, which is sandwiched by a first case and a second case, from being squeezed to a gap between the first case and the second case.
According to the present invention, a pressure detection apparatus having a wall portion is provided at opposite side of the pressure detection chamber with respect to the O-ring. The wall portion has a first surf ace and a second surf ace defining a corner portion with the first surface. Here, a radius of curvature of the corner portion is set less than 0.1 mm. As a result, it can restrict the O-ring from being squeezed into a gap between a first case and a second case at the corner portion.
According to another aspect of the present invention, a pressure detection apparatus having a wall portion being provided at opposite side of the pressure detection chamber with respect to the O-ring. The wall portion has a first surface and a second surface defining a corner portion with the first surface. Here, a distance between an end of the first surface and a flat surface, which is the same as the second surface, is set less than 0.1 mm. As a result, it can restrict the O-ring from being squeezed into a gap between a first case and a second case at the corner portion.
According to still another aspect of the present invention, a pressure detection apparatus having a wall portion being provided at opposite side of the pressure detection chamber with respect to the O-ring. The wall portion has a first surface and a second surface defining a corner portion with the first surface. The second case sandwiches the O-ring with the first case by contacting the second surface. Here, the corner has an O-ring squeezing protection member provided at the corner portion to contact with the second surface, and projected from the first surface toward the O-ring. As a result, O-ring squeezing protection member can restrict the O-ring from being squeezed into a gap between a first case and a second case at the corner portion.
According to further still another aspect of the present invention, a method of manufacturing a pressure detection apparatus, comprising the steps of assembling the first case and a second case to define the pressure detection chamber, with sandwiching the O-ring between the first case and the second case at a peripheral portion of the pressure detection chamber. In this assembling step, the O-ring is inserted to the groove portion; and the O-ring is pressed to cover the groove portion with the second case with crushing the projection portion of the corner portion. According to this method, since the projection portion is expanded as a result of being crushed, the crushed projection portion can restrict the O-ring from being squeezed into a gap between a first case and a second case at the corner portion.